Fiber optic sensor systems using phase generated carriers carry information of interest in a phase of an optical signal. The “carrier” is manifested as an intentional sinusoidal phase modulation of the optical wave which is used by a sensor—essentially an interferometer—to sense some type of information (e.g., pressure). The sensed information transduced by the optical sensor adds an additional phase modulation to the optical signal. When the optical signal is received at a remote location, usually via a fiber optic means, the sensed information must be extracted from the optical signal—comprising the carrier and the sensed information—in a process commonly called demodulation. Demodulation involves first converting the amplitude of the analog optical signal to an electrical signal. In digitally oriented systems the analog electrical signal is next passed through an analog to digital converter (ADC) after which the desired sensed information can be extracted via digital means.
In a Frequency Division Multiplex (FDM) system more than one optical carrier is combined through an array of multiple sensors. As such, the electrical signal is much more complex. It is somewhat analogous to an FM cable audio system where many carriers or channels are contained on a single conductor. A technique was previously described in a homodyne system whereby a discrete Fourier transform (DFT) typically, though not necessarily, implemented as a fast Fourier transform (FFT) could be used to demodulate a number of sensors each with its own carrier. Typically, in such a system, increasing the number of sensors returned on a single fiber requires adding a new carrier for each new sensor. The computing resources required to perform demodulation in such a system, may increase dramatically as the number of sensors that are carried is increased.